Simultaneous vision refers to the class of bifocal contact lenses in which optical power for distance vision and near vision are positioned simultaneously within the pupil area of a user""s eye. The conventional clinical understanding for simultaneous vision is that a bifocal lens projects both distance and near images simultaneously onto the retina. Depending on the viewing distance of the object of regard, one of the images is in focus, and the other image is out of focus. It is believed that the brain is able to disregard the irrelevant out-of-focus image and to process only the relevant in-focus image. Therefore, whether an object is at distance or near locations, the lens is still able to provide levels of vision that may be acceptable to many patients.
There have been attempts to provide a simultaneous vision contact lens in the past. One type of simultaneous vision lens is the concentric zone bifocal lens in which the distance and near powers form two concentric optical zones. These lenses have included center distance or center near configurations. The dimensions of the two zones are chosen such that approximately equal areas of distance and near power are provided within the pupil area of the eye. This lens includes the advantage of providing the user with two relatively large optical areas on the lens. However, because the dimensions of a user""s pupil vary from user to user and in response to ambient light levels, the relative areas of distance and near power can deviate significantly such that near vision or distance vision may be favored at the expense of the other. Since this dependence on pupil size is not under the conscious control of the user, this distance or near bias may not be appropriate for the vision requirements of a particular user.
To reduce this dependence on pupil size, additional concentric zones may be incorporated into the lens, see e.g., U.S. Pat. No. 4,704,016 (Cohen). The total bifocal optical zone of such a lens consists of a series of concentric annuli which must be within the pupil area of the eye and which alternately provide the distance and near power. But as the number of annuli increases, the width of each annulus must decrease if the zone (or at least a significant portion of it) is to remain within the pupil area. This can cause the optical quality of the distance and near powers to degrade because of the reduced dimension of each zone. In addition, undesirable edge effects are created by the boundaries between the various zones. This optical degradation can offset the potential advantages of reducing the dependence on pupil size by the incorporation of the multiple zones.
Another type of simultaneous vision lens includes within the bifocal optical zone the use of an aspheric surface which provides a continuous gradient of optical power over a selected range of powers. The steepness of the power gradient must be designed to provide the desired difference between the near power value and the distance power value (that is, the desired bifocal add power) within the pupil area of the eye. Therefore, the visual performance of the aspheric simultaneous lens design is limited by the same dependence on pupil size as in the concentric zone design. Moreover, by attempting to provide all power corrections over the full range of values between distance and near, the aspheric design compromises the quality of the vision provided at any one particular power value.
An example of an aspheric lens is U.S. Pat. No. 5,754,270 (Rehse et al.). The ""270 patent discloses a lens having a centrally located aspherical first optical zone, a second aspherical concentric optical zone and a transition zone that provides a rapid power shift between the first zone and the second zone. This lens suffers from the disadvantage of compromising a user""s visual acuity at a particular power value because it includes ranges of powers rather than zones with selected powers.
Yet another type of simultaneous vision lens is based on diffractive optics. In theory this lens provides nearly equal levels of distance and near vision with minimal dependence on pupil size, but in practice the clinical acceptance of diffractive bifocal contact lenses has been relatively low. It is not clear whether this low acceptance is primarily due to limitations in the inherent quality of diffractive optics or due to the complexity of the diffractive optical element which is quite difficult to manufacture.
To develop a better-performing design, it must first be recognized that the conventional explanation for simultaneous vision described above may be misleading. By describing simultaneous vision in terms of a near image and a distance image, the conventional theory assumes that there are two distinct retinal images which the brain can somehow distinguish and process separately. At any particular moment the eye is looking at a specific object of regard which is at a particular viewing distance. With all simultaneous vision lenses a partially degraded image of that object is projected onto the retina. The consequence of this image degradation is a loss of visual information (less signal, more noise), and the quality of the degraded image may or may not be acceptable to the patient. The clinical effects of this degradation may be measured objectively in terms of reduced visual acuity and contrast sensitivity. The subjective effects of the degradation are perceived by the patient in various ways which are collectively referred to as subjective blur. Therefore, when wearing a simultaneous vision lens, the patient may not be selecting between separate distance and near images. Rather, in the presence of subjective blur the patient may be attempting to function with the reduced level of visual information that is provided by a degraded image.
The visual system does have the ability to filter out some of the noise, and many patients demonstrate a tremendous potential to adapt to subjective blur. In some patients the adaptation is so complete that they may not report any subjective blur even though by objective measures their vision may be obviously compromised. However, the opposite situation may occur where an objective assessment indicates normal vision performance, but the patient paradoxically complains of poor vision.
Therefore, there is a need for an improved simultaneous lens design that maximizes the available visual information for objects of regard at distance and at near locations and concurrently minimizes visual disturbances.
The present invention provides an optimized lens construction that provides for the reduction of visual disturbances that result from the transitions between areas as formed in past lenses while providing an enhanced visual acuity over a range of distances. There is also a need for a lens that combines the positive features of a concentric design with the positive features of an aspheric design in a unique integrated design that minimizes the disadvantages of each.
Briefly stated, the present invention provides a lens having a plurality of vision areas. The plurality of areas including a first vision area, a second vision area surrounding the first vision area, and a third vision area surrounding the second vision area. The first vision area having a first power, the second vision area having a range of powers, and the third vision area having a second power distinct from the first power. One of the first, second and third vision areas having an aspheric surface designed to provide a monotonic gradient in power and the other areas having either spherical surfaces to provide single power values or aspheric surfaces designed to correct optical aberrations within these single power areas.
The present invention also provides a lens having a plurality of vision areas. The areas include a first vision area, a second vision area, and a third vision area. The second vision area is between the first vision area and the third vision area. The first, second and third vision areas defining a portion of a surface profile of the lens wherein the direction of concavity does not change even though the power profile may show adjoining areas of single power values and gradient power values.
The present invention is also directed to an ophthalmic kit. The kit includes a sterile packaged contact lens in a bacteriostatic solution in accordance with the present invention. The kit can include the lens secured in a vial or a blister package.
According to yet another aspect of invention, a method of using a contact lens is provided. According to a first step, a user places the contact lens over a pupil of the user""s eye. The contact lens has a transition from a first vision area having a first power and a second vision area having a second power.
As used herein, the term xe2x80x9clensxe2x80x9d is intended to be interpreted broadly to include a wide variety of lenses including contact lenses and intraocular lenses.
As also used herein, the term xe2x80x9cpowerxe2x80x9d is intended to be interpreted broadly to include a single power or an average power.
As further used herein, the term xe2x80x9crange of powersxe2x80x9d is intended to be interpreted broadly to include a series of substantially continuous or non-continuous powers.
As used herein, the term xe2x80x9careaxe2x80x9d is intended to be interpreted broadly to include zones or regions.
As used herein, the term xe2x80x9cvision areaxe2x80x9d is intended to include area that contributes to the vision of a user.